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Results for “Postural control”

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PubMed1985

Effects of postural bias during support surface displacements and rapid arm movements.

The purpose of this study was to evaluate body-sway characteristics during anticipatory and reactive postural compensation. Mechanisms of postural control were studied during self-initiated rapid arm movements (RAMs) and unexpected support surface displacements (SSDs). Ten healthy subjects, 5 men and 5 women with a mean age of 28 years, were blindfolded and stood symmetrically on a moveable force platform or with weight shifted right (R) or left (L). Averaged electromyographs were obtained from L anterior deltoid, L ipsilateral biceps femoris (BFi), R contralateral biceps femoris (BFc), R quadriceps (Q), R medial gastrocnemius (G), and R tibialis anterior (TA) muscles. During SSD, the relative timing of distal-proximal synergists was altered during all biased postures. In L biased standing, functional pairs, TA-Q and G-BF, discharged at their shortest latencies. Anterior deltoid onset times during RAM were most preparatory during R weight shift. Sway latencies were shorter also in biased standing. Absolute sway latency, peak sway, and time-to-peak sway were significantly longer in SSD conditions in comparison with RAM. When disturbances in balance cannot be predicted, lower extremity preloading facilitates contralateral muscle-discharge patterns at shorter latencies. In some neurological conditions that result in incorrect body alignment, the mechanical effects of postural bias rather than the abnormal control mechanisms may at least contribute to alterations in the postural response. These results provide a basis for evaluating balance in patients with neurological deficit.

Adult↗

PubMedDate not supplied

Closed-loop, estimator-based model of human posture following reduced gravity exposure.

A computational and experimental method is employed to provide an understanding of a critical human space flight problem, posture control following reduced gravity exposure. In the case of an emergency egress, astronauts' postural stability could be life saving. It is hypothesized that muscular gains are lowered during reduced gravity exposure, causing a feeling of heavy legs, or a perceived feeling of muscular weakness, upon return to Earth's 1 g environment. We developed an estimator-based model that is verified by replicating spatial and temporal characteristics of human posture and incorporates an inverted pendulum plant in series with a Hill-type muscle model, two feedback pathways, a central nervous system estimator, and variable gains. Results obtained by lowering the variable muscle gain in the model support the hypothesis. Experimentally, subjects were exposed to partial gravity (3/8 g) simulation on a suspension apparatus, then performed exercises postulated to expedite recovery and alleviate the heavy legs phenomenon. Results show that the rms position of the center of pressure increases significantly after reduced gravity exposure. Closed-loop system behavior is revealed, and posture is divided into a short-term period that exhibits higher stochastic activity and persistent trends and a long-term period that shows relatively low stochastic activity and antipersistent trends.

Adult↗

PubMed1987

[Posturography should be included in the vertigo test].

After a brief review of different systems involved in postural control, we describe a method of posturography for exploring vestibulospinal pathways, in which postural oscillations of subject standing on a platform are recorded with eyes open then with eyes closed, and in different head and gaze positions. In normals, only closing of eyes interferes significantly with balance. Posturography is important in vertigo examinations, because it can show: vestibuloocular and vestibulospinal pathway lesions, associated or not; whether there is compensation for imbalance by visual input; cervical origin of vertigo, if any; and, in acute vestibular deficit, that good test results suggest a favorable prognosis.

Adult↗

PubMed1992

Perception of motion and position relative to the earth. An overview.

Results of the five experiments are consistent with the following generalizations. Canal-mediated turn perception (pitch, roll, or yaw) in earth-horizontal or earth-vertical plane, is suppressed in direct relationship to the magnitude of a linear acceleration vector lying in the plane of a responding canal when the magnitude of the linear vector is constant or increasing and when its direction is either fixed or rotating in the same direction as the concomitant canal signal. Canal-mediated turn perception (pitch, roll, or yaw) is not suppressed by a coplanar linear vector that is counterrotating relative to the canal signal. Change in perceived attitude (pitch, roll, or yaw) is very sluggish in the absence of concordant canal information; attitude change may not be an immediate otolith-mediated perceptual event but a slowly developing perception dependent upon cognitive appreciation of an immediate otolith angular position signal. Otolith phasic neural units, unreinforced by appropriate canal signals, may contribute more to a brief linear velocity component in perception than to rate of attitude change. Otolith-mediated attitude perception within a given earth-vertical plane can be distorted by strong coplanar angular velocity canal information. Once distorted, return to veridical attitude perception can be gradual because, in the absence of complimentary canal or visual information, recovery is dependent upon relatively slow cognitive appreciation of a prevailing otolith position signal. Several attractive hypotheses relating to the dynamics of attitude perception can only be tested by substantially more data on the dynamics of spatial orientation perception. Most of our objectives cannot be achieved without models that yield valid prediction of the dynamics of spatial orientation perception. All of the observations in these experiments were carried out in darkness, or, in the simulated catapult experiment, without external visual reference. Various forms of visual information will change the dynamics of spatial orientation perception. My discussion has been limited to consideration of the vestibular system, as though the canal and otolith systems completely controlled the dynamics of spatial orientation perceptions. Obviously other partners in the dynamics of postural control, including vision, proprioception, and expectation, must be included in this challenging field of research. Dedication to stereotyped ideas about objectivity in the 20th century has hindered advancement of knowledge on the dynamics of spatial orientation perception relative to rate of progress achieved by several scientists of the 18th and 19th centuries, who provided word pictures of perceived motions and tilts along with descriptions of the motions that engendered the pictures.(ABSTRACT TRUNCATED AT 400 WORDS)

Gravitation↗

PubMed2005

Compatibility of postural behavior induced by two aspects of visual feedback: time delay and scale display.

Fourteen healthy adults were tested to assess the potential influence on stance maintenance of two parts of the visual feedback technique (display scale and time delay). The task consisted in their keeping a spot on the screen representing their center of pressure, CoP (i.e. successive points of application of the ground reaction forces detected by the force platform on which they were standing) to a minimum size. The analysis focused on elementary motions computed from the complex CoP trajectories, that is the horizontal motion of the center of gravity (CoG(h)) and the difference between the CoP and the vertical projection of the center of gravity (CoP-CoG(v)). The former is recognized as the main variable in postural control, and several interesting features can be extracted from the latter. The results indicate that setting a delay and increasing the display scale induce substantial reductions in CoP-CoG(v) and CoG(h) displacements, respectively. Interestingly, when the two effects are combined, these single effects cohabit quite happily. Fractional Brownian motion modeling of these trajectories revealed clearly that, in each case, these effects originate principally from poor or improved control, respectively. This feature confirms that these elementary motions are involved differently in the postural system and that study of the complex CoP might not be of great interest. By generating opposing but complementary trends, the visual feedback technique should thus be perceived as a promising tool for inducing particular postural behavior in healthy and disabled individuals.

Adult↗

PubMed2001

Postural dynamics: clinical and empirical implications.

OBJECTIVE: To provide a rationale for the examination of posture from a dynamic (behavioral) perspective and to relate the vertebral subluxation to postural instability and motion sickness via inefficiency. DATA COLLECTION: A manual search of available reference texts and a computer search of literature from Index Medicus, PsycINFO, and ISI Science Citation Index Expanded were collected with an emphasis on postural dynamics, vertebral subluxation, and motion sickness. RESULTS: Evidence linking behavioral and health research has emerged from the study of posture and postural dynamics. Studies examining the relation between postural control and motion sickness have shown that motion sickness is preceded and predicted by postural instability. Motion sickness is characterized by maladaptive response to unusual motion events. The symptoms are nonspecific and variable. Although the Postural Instability theory of motion sickness predicted that instability should precede sickness, it did not make any claims regarding the symptoms associated with it. Chiropractic literature has emphasized the effects of vertebral subluxation on neurologic dysfunction. Vertebral subluxation is a condition that is postulated to interfere with neurologic processes and may influence organ system function and general health. As in the case of motion sickness, symptoms are nonspecific and variable (and in some instances the person may have no symptoms). So what do these disorders have in common? In each instance the disruptions lead to inefficiency in the system. CONCLUSION: Given this potential commonality, we propose that some of the methods used by behavioral researchers to study postural dynamics may also be of great utility to health care practitioners and psychologists alike. Furthermore we propose that this link will provide a framework that will allow scientists to address seemingly intractable problems such as motion sickness or subluxation.

Biomechanical Phenomena↗

PubMed2004

The scaling of postural adjustments during bimanual load-lifting in traumatic brain-injured adults.

Previous postural studies of traumatic brain injury (TBI) patients have been limited to identifying deficits in static and quasi-dynamic postural control tasks such as weight shifting. In this study, we examined whether or not patients with TBI are able to scale adequately their postural adjustments during the performance of the dynamic task of bimanual load-lifting. An age matched group of healthy adults served as controls. We used the Tetrax posturography system that calculates a stability score (ST) based on fluctuations in vertical ground reaction forces, normalized for body weight. During quiet standing, the ST scores of the TBI group were significantly higher than the control group. Forward weight shift and percentage change in the vertical ground reaction forces (lift postural adjustment (LPA) and post-lift postural adjustment (PLPA) scores) linearly increased with increasing load weight in both healthy and TBI subjects. Group differences were found in the magnitude of forward weight shift but not in the relative increase of the LPA and PLPA scores during the lifting and post-lifting phases respectively. The forward weight shift of the TBI group was lower-than-normal and asymmetrical--there was significantly less forward weight shift on the more affected than on the less affected limb. In addition, a significant amplitude coupling was found between the scaling of the weight shift of the heel and forefoot of each limb. However, no coupling was found between the weight shift amplitudes of homologous parts of both limbs in the TBI group. The results showed that scaling based on prior experience was preserved in the TBI group, though some TBI subjects demonstrated absent scaling in either the more affected or less affected heel or forefoot. The differences between the normal and TBI groups in postural adjustments are not necessarily a sign of pathology; rather they may represent a deliberate choice of the central nervous system to counteract predictable disturbances.

Adult↗

PubMed2000

Effects of gymnastics expertise on the perception of body orientation in the pitch dimension.

The purpose of this study was to investigate how experts in motor skills requiring a fine postural control perceive their body orientation with few gravity based sensory cues. In Experiment 1, expert gymnasts and controls had to detect their body tilt when pitching at a velocity of 0.05 deg.s(-1), in two conditions of body restriction (strapped and body cast altering the somatosensory cues). Contrary to the experts, the controls exhibited a larger body tilt when totally restrained in the body cast. In Experiment 2, subjects had to estimate their Subjective Postural Vertical (SPV) starting from different angles of pitch tilt. The controls exhibited significant errors of SPV judgement whereas the experts were very precise. These results suggest that 1) somatosensory cues are more informative than otolithic cues for the perception of body orientation, and 2) the efficiency of otolithic and/or interoceptive inputs can be improved through a specific training to compensate for the lack of somatosensory cues.

Adolescent↗

PubMed2001

Spatial orientation and balance control changes induced by altered gravitoinertial force vectors.

To better understand the mechanisms of human adaptation to rotating environments, we exposed 19 healthy subjects and 8 vestibular-deficient subjects ("abnormal"; four bilateral and four unilateral lesions) to an interaural centripetal acceleration of 1 g (resultant 45 degrees roll-tilt of 1.4 g) on a 0.8-m-radius centrifuge for periods of 90 min. The subjects sat upright (body z-axis parallel to centrifuge rotation axis) in the dark with head stationary, except during 4 min of every 10 min, when they performed head saccades toward visual targets switched on at 3- to 5-s intervals at random locations (within +/- 30 degrees) in the earth-horizontal plane. Eight of the normal subjects also performed the head saccade protocol in a stationary chair adjusted to a static roll-tilt angle of 45 degrees for 90 min (reproducing the change in orientation but not the magnitude of the gravitoinertial force on the centrifuge). Eye movements, including voluntary saccades directed along perceived earth- and head-referenced planes, were recorded before, during, and immediately after centrifugation. Postural center of pressure (COP) and multisegment body kinematics were also gathered before and within 10 min after centrifugation. Normal subjects overestimated roll-tilt during centrifugation and revealed errors in perception of head-vertical provided by directed saccades. Errors in this perceptual response tended to increase with time and became significant after approximately 30 min. Motion-sickness symptoms caused approximately 25% of normal subjects to limit their head movements during centrifugation and led three normal subjects to stop the test early. Immediately after centrifugation, subjects reported feeling tilted 10 degrees in the opposite direction, which was in agreement with the direction of their earth-referenced directed saccades. Postural COP, segmental body motion amplitude, and hip-sway frequency increased significantly after centrifugation. These postural effects were short-lived, however, with a recovery time of several postural test trials (minutes). There were also asymmetries in the direction of postcentrifugation COP and head tilt which depended on the subject's orientation during the centrifugation adaptation period (left ear or right ear out). The amount of total head movements during centrifugation correlated poorly or inversely with postcentrifugation postural stability, and the most unstable subject made no head movements. There was no decrease in postural stability after static tilt, although these subjects also reported a perceived tilt briefly after return to upright, and they also had COP asymmetries. Abnormal subjects underestimated roll-tilt during centrifugation, and their directed saccades revealed permanent spatial distortions. Bilateral abnormal subjects started out with poor postural control, but showed no postural decrements after centrifugation, while unilateral abnormal subjects had varying degrees of postural decrement, both in their everyday function and as a result of experiencing the centrifugation. In addition, three unilateral, abnormal subjects, who rode twice in opposite orientations, revealed a consistent orthogonal pattern of COP offsets after centrifugation. These results suggest that both orientation and magnitude of the gravitoinertial vector are used by the central nervous system for calibration of multiple orientation systems. A change in the background gravitoinertial force (otolith input) can rapidly initiate postural and perceptual adaptation in several sensorimotor systems, independent of a structured visual surround.

Acceleration↗

PubMed2001

Delayed stochastic differential model for quiet standing.

A physiological quiet standing model, described by a delayed differential equation, subject to a white noise perturbation, is proposed to study the postural control system of human beings. It has been found that the white noise destabilizes the equilibrium state, and inertia accelerates the destabilizing process, and that the position of a person is detected and processed by the person's nervous system with a delay. This paper focuses on the analysis of Hopf bifurcation and its stability in this context. Based on the analytical predictions confirmed by numerical simulations, it has been shown that the posture of a person is controlled in such a way that possible amplitude oscillations are minimized.

Computer Simulation↗

PubMed2002

Neck vibration causes short-latency electromyographic activation of lower leg muscles in postural reactions of the standing human.

To study how quickly cervical proprioceptive information induced muscular responses in the lower leg to control posture in the standing human we investigated lower leg muscle electromyography and force-plate data from 10 healthy normal subjects, when perturbed by posterior neck muscle vibration. At the onset of vibration the tibialis anterior muscle was activated at latencies of 70-100 ms whilst the triceps surae muscle was inhibited at the same latencies. At offset the opposite pattern was observed. These findings suggest that a short-latency integrative system, rather than a direct reflex, mediates the cervical influence on posture. The short latencies also imply that activation of postural muscles in response to vibration towards the neck muscles occurs faster than would be expected if it was caused only by a perceptive illusion of movement.

Adult↗

PubMed2006

Long-term effects of 6-week whole-body vibration on balance recovery and activities of daily living in the postacute phase of stroke: a randomized, controlled trial.

BACKGROUND AND PURPOSE: The long-term effects of 6-weeks whole-body vibration, as a novel method of somatosensory stimulation, on postural control and activities of daily living were compared with those of 6 weeks of exercise therapy on music of the same intensity in the postacute phase of stroke. METHODS: Fifty-three patients with moderate to severe functional disabilities were randomized within 6 weeks poststroke and within 3 days after admission to a rehabilitation center to either whole-body vibration or exercise therapy on music in addition to a regular inpatient rehabilitation program. The whole-body vibration group received 4x45-second stimulation on the Galileo 900 (30-Hz frontal plane oscillations of 3-mm amplitude) for 5 days per week during 6 weeks. The exercise therapy on music group received the same amount of exercise therapy on music. Outcome variables included the Berg Balance Scale, Trunk Control Test, Rivermead Mobility Index, Barthel Index, Functional Ambulation Categories, Motricity Index, and somatosensory threshold at 0, 6, and 12 weeks follow up. RESULTS: At baseline, both groups were comparable in terms of prognostic factors and outcome measures. Both at 6 and 12 weeks follow up, no clinically relevant or statistical differences in outcome were observed between the groups. No side effects were reported. CONCLUSIONS: Daily sessions of whole-body vibration during 6 weeks are not more effective in terms of recovery of balance and activities of daily living than the same amount of exercise therapy on music in the postacute phase of stroke.

Activities of Daily Living↗

PubMed2004

Mirror versus stationary cross feedback in controlling the center of foot pressure displacement in quiet standing in elderly subjects.

OBJECTIVE: To investigate the effect of mirror feedback on postural control during quiet standing in elderly adults. DESIGN: Before and after intervention trials. SETTING: Pneumology center in France. PARTICIPANTS: Eleven elderly adults (mean age, 70.7+/-4.6 y; mean body weight, 64.5+/-15.0 kg; mean height, 161.4+/-12.0 cm). INTERVENTIONS: Participants were asked to stand upright, as immobile as possible, in 2 eyes-open and mirror-feedback conditions. The latter experimental condition consisted of supplying the subjects with their frontal reflection by positioning a mirror in front of them. MAIN OUTCOME MEASURES: Foot center of pressure (COP) displacements in the mediolateral (ML) and anteroposterior (AP) directions were recorded using a force platform. RESULTS: The mirror-feedback condition had different effects on postural sway, depending on the direction: range, variability, and maximal instantaneous speed of the COP displacements decreased in the ML direction, whereas these effects remained unchanged in the AP direction. CONCLUSIONS: This study provided evidence that mirror feedback may put elderly adults at lower risk of falling.

Aged↗

PubMed2006

Ankle force and rate of force production increase following high intensity strength training in frail older adults.

BACKGROUND AND AIMS: The most common cause of accidental injury and death in people over age 65 results from impacts associated with falling. Balance impaired older adults have poorer balance control than healthy young adults or healthy older adults. Lack of sufficient lower extremity strength and inability to rapidly produce muscle force may contribute to diminished balance control in the elderly. This study evaluated the effect of a 10-week high intensity strength-training program targeting key lower extremity muscles for the purpose of improving postural control in frail older adults. METHODS: Thirteen experimental and fourteen control subjects, all balance impaired older adults were evaluated in response to unexpected platform perturbations that simulated slips. RESULTS: Following strength training the experimental group was significantly stronger than the control group. Mean ankle moments improved in the experimental group following strength training during forward sway (Right: p=0.067, Left: p=0.009) and backward sway (Right: p=0.031, Left: p=0.058). For the backward sway condition the ankle rate of torque production increased significantly in the experimental group (Right: p=0.016, Left: p=0.031). CONCLUSIONS: Enhancement of lower extremity strength contributed to improvements in balance stability demonstrated by greater ankle force production, in response to balance threats.

Accidental Falls↗

PubMed2001

First-order statistics of human stabilogram.

We investigated the statistical properties of the centre of pressure (COP) vector during quiet standing, as measured on a force platform. To derive a statistical model for the data, the COP vector, locally averaged COP, and deviations from the average COP were analysed. Whereas indefinite multimodal distributions for the components of the COP were observed, the density functions of deviation from the averaged COP had reproducible properties. The anterior-posterior and mediolateral components of the deviations had in common that they were correlated variables with a non-circular statistic. The main axes of the equiprobability density curves were rotated with respect to the natural anterior-posterior and mediolateral directions. By means of more detailed statistical analysis of the data, two distinct populations of subjects were identified. In some cases we have found Gaussian distributions of the components of deviation from the average COP. In most cases the statistics was non-Gaussian. The average contrast, a new dimensionless characteristic quantity, independent of platform calibration, was introduced as a useful indicator of non-Gaussian effects in the postural control system.

Humans↗

PubMed2002

Down training of the elderly soleus H reflex with the use of a spinally induced balance perturbation.

The purpose of this study was to determine the ability of the elderly central nervous system to modulate spinal reflex output to functionally decrease a spinally induced balance perturbation. In this case, the soleus H reflex was used as the source of perturbation. Therefore, decreasing (down training) of the soleus H reflex was necessary to counteract this perturbation and to better maintain postural control. In addition to assessing the effect of this perturbation on the H reflex, static postural stability was measured to evaluate possible functional effects. Ten healthy young subjects (age: 27.0 +/- 4.6 yr) and 10 healthy elderly subjects (age: 71.4 +/- 5.1 yr) participated in this study. Subjects underwent balance perturbation on 2 consecutive days. On day 1 of perturbation, significant down training of the soleus H reflex was demonstrated in both young (-20.4%) and elderly (-18.7%) subjects. On day 2 of perturbation, significant down training of the soleus H reflex was again demonstrated in both young (-24.6%) and elderly (-21.0%) subjects. Analysis of static stability after the 2 days of balance perturbation revealed a significant 10.1% decrease in the area of sway in elderly subjects. In conclusion, this study demonstrated that healthy, elderly subjects compared with young subjects were equally capable of down training the soleus H reflex in response to a balance perturbation. Furthermore, the improvement in static stability through balance training may provide further evidence that balance can be retrained and rehabilitated in subjects with decreased reflex function.

Adult↗

PubMed2005

Postural behavior in children born preterm.

The present paper presents clinical and neurophysiological data of postural behavior in preterm children without CP. Clinical follow-up studies of preterm infants until toddler and school age have reported that low-risk preterm infants may have atypical postural behavior in terms of reduced amount of rotation during crawling, delayed dynamic balance, delayed onset of and a poor quality of early walking behavior. At school age, dysfunctions such as problems in standing on one leg and poor hopping are reported. Neurophysiological data of postural control at early age indicated the presence of a dysfunction in the capacity to modulate postural activity, and the postural activity has been characterized by temporal disorganization of EMG responses. Postural responses to goal-directed reaching in supine lying have been recorded and analyzed in terms of the total body center of pressure. In this study, preterm infants show less mobile postural behavior compared with full-term infants. In infancy, the less mobile postural behavior seemed to be adequate as it was related to better goal-directed reaching quality, but the results indicated that the relatively immobile postural behavior during reaching in early age was related to less favorable neuromotor behavior in school-age.

Central Nervous System↗

PubMed1999

[Time constant of forward body sway induced by downward optokinetic stimulus].

Forward body sway induced by a downward optokinetic stimulus (OKS) was observed in 38 healthy subjects. The downward OKS was generated by a moving random dot pattern projected onto a half-pipe screen 2 m in diameter and was provided by a rectangular-like step function with velocities of 10, 20, 30 and 40 deg/sec. A fixation target was set by a red laser spot projected onto the screen in front of the subjects. As an additional stimulatory condition, 20 deg/sec of OKS with no fixation target was employed. The induced forward body sway was measured by a force-detecting platform as displacement of the center of gravity (COG). The gradual forward shift of COG followed by the plateau state was closely akin to a graphical representation of an equation of the first order lag time. As OKS velocities increased, the plateau level increased. Curve fitting analysis using a computer was employed to establish an approximation equation of the first order lag time. This analysis showed that the time constant of the optokinetic spinal response system was approximately 15 sec and the value of the time constant was independent of OKS velocity. Based on this long time constant, we concluded that the postural readjustment induced by OKS mainly plays a role in the low frequency range of human postural control.

Eye Movements↗